M634 Experimental High-Powered Semi-Armor-Piercing

M634 Experimental High-Powered Semi-Armor-Piercing, abbreviated as M634 X-HP-SAP and also known as the 9.5×40mm KURZ,[1][note 1] is a 9.5×40mm rifle cartridge made specifically for the BR55 series and BR85 series.[2]

Performance-wise, this round is accurate enough that the 2× scope on the Battle Rifle is useful. Even when fired in three-shot bursts, the round produces little recoil resulting in very little muzzle lift. It is more effective against both shielded and unshielded Covenant personnel than the M118 7.62×51mm round, as the increased accuracy leads to an increased kinetic energy of the round leads to faster shield depletion and increased damage to unshielded enemies. Overall, the M634 X-HP-SAP round provides good accuracy, controllability, and effectiveness against all personnel.

As designated in its name, the M634 X-HP-SAP is an experimental round. It uses a special propellant that allows it to achieve a higher muzzle velocity than the M118 7.62×51mm round while using a smaller cartridge. It is also semi-armor-piercing, meaning that it mixes the properties of an armor piercing round with the properties of another type of round. The second type is unknown, though it is most likely similar to the M225 SAP-HE used in the M6 Series.

Unlike most ammunition types in the Halo games, this is not a real-life ammo type, the closest comparison being the 9×39mm special purpose round. Designed in the Soviet Union, this round was designed to defeat body armor at ranges closer than 100 meters, and be subsonic, so it can be easily used in suppressed firearms. In fact, most weapons firing it have an integrated silencer. However, the M634 does not appear to be subsonic in any cases, instead intended for high-velocity and long range marksmanship. The M634 is likely the result of the human inclinations towards bigger things (leading to the 9.5 mm bullet) and technological manipulation (leading to the experimental propellant). It's also possible the large caliber, while overkill by current standards, is required to defeat the advanced body armor of the Insurrectionists, and later, the Covenant.